Polymerization inhibitor



United Sites Patent 2,861,041. PoLvMERIzATioN INHIBITOR Herbert H. Nelson, Dickinson, Tex., assignor to Monsanto Chemical Company, St. Louis, Mo., a corporatioii of Delaware 7 No Drawing. ApplicationMay 4, 1954 Serial No. 427,669

2 Claims. (Cl. 252-1) This invention relates to the inhibition of polymerization. In one embodiment, it pertains to the inhibition of undesirable polymer growth in processing equipment. Specifically, it is concerned with a method for the stabilization of diacetylene, or of mixtures containing diacetylene, against polymerization and the stabilized compositions so produced.

If acetylene is produced from hydrocarbons, e. g., by the well known electric arc process or by thermal decomposition or dissociation, the acetylene-containing gas mixture produced generally contains diacetylene as well, in amounts ranging from as little as 0.05% to as much as 5%. The purification of such an acetylenic gas mixture is usually accomplished by the selective action of suitable solvents. A great number and variety of solvents have been proposed and are effectively employed in welldeveloped purification processes. However, in these conventional methods of absorption and stripping, the gas mixture is exposed to conditions of temperature and pressure under which some of the diacetylene present polymerizes, and provision must be made in all such processes for periodic removal of the diacetylene polymers to prevent their excessive build-up in the solvent in the absorption step. This requires additional, specialized filtration equipment as Well as added process steps which are costly with regard to both time and capital expense. Frequently, too, the diacetylene polymer collects in the less accessible parts of the system, fouling up equipment lines, columns, and the like. Usually, this particular polymer is of such a small particle size that it plugs the filter used for separating it, so that only a small amount can be filtered in each operation and an inordinate length of time is required to wring the filter cake dry.

Methods have been proposed for removal of diacetylene from the gas stream, but these are cumbersome and expensive since they require additional process steps prior to the usual solvent purification operation which utilizes special equipment and significant quantities of speci..l chemicals for treating purposes.

It is an object of the present invention, therefore, to provide a method whereby undesirable polymer growth in the solvent purification of acetylene is inhibited.

It is a further object of the invention to provide a method for stabilization of diacetylene against polymerization.

It is a still further object of the invention to provide novel stabilized composition comprising diacetylene, a solvent therefor, and an added polymerization inhibitor which do not polymerize when subjected to conditions under which such compositions lacking the inhibitor polymerize readily and rapidly.

Other objects and advantages of the invention will be apparent from the following description and the appended claims.

According to the invention, diacetylene contained in a solvent is stabilized against polymerization by the addition thereto of small quantities of pyridine. The composition comprising diacetylene, a solvent therefor,

- 2 and a minor amount'of pyridine-will not exhibitany significant polymerformation on prolonged periods" of sto r age or when subjected to the temperatures commonly encountered in solvent purification systems for acetylene purification.

The following example illustrates the invention but is not to be construed as limiting it in any manner.

EXAMPLE 1 Diacetylene was generated by dropping 40% sodium hydroxide into a well-stirred solution of-1,4-dichlorobutyne in ethanol at a temperature of approximately C. The productgas .Was passed through Dry Ice) traps and then allowed to bubble through a fritted gas" bubbler into technicab'grade' butyrolactone at room temperature to make a stock solution of 0.3 g. of diacetylene per milliliter of solution. In the polymerization tests, 20 ml. of a test mixture containing a known amount of the diacetylene stock solution, butyrolactone, water, and a weighed amount of the inhibitor were introduced into a thickwalled test tube. The mixture was frozen and the end of the test tube was drawn ofi in a torch flame to make a sealed ampoule. The sealed ampoules were wrapped in bronze screen and placed in an oven maintained at C. for 16 hours, after which they were removed and inspected for polymer content. Blanks were run in which only butyrolactone and mixtures of butyrolactone, water and diacetylene were present. Results of a series of such tests are presented in Table I.

Table I Test Test Mixture Condition of Test Mixture No.

1 50% Butyrolaetone-50% H2O. Usual straw color; perfectly clear; unchanged. 2 Same as in Test N o. 1 above Pale yellow; perfectly clear plus 1% pyridine. solution. 3 50% BL 50% H2O plus Reddish brown suspension of 0.25% diacetylene. polymer; fairly heavy ppt. of

finely divided material. 4 Same as in Test N o. 3 above Medium red-brown suspenplus 0.01% pyridine. sion; only trace of ppt. settled out. 5 Same as in Test No. 3 above Dark wine color; very small plus 0.1% pyridine. amount of cellophane-type solid on surface; no visible D1 6 Same as in Test No. 3 above Very dark wine color; no visiplus 1% pyridine. ble ppt; tiny amount of floating cellophane-type solids. 7 50% EL -50% H2O plus Heavy brown ppt. settled on 0.5% diacetylene. bottom of tube; liquid also full of suspended polymer. 8 Same as Test No. 7 above plus Very dark Wine-red solution; 0.1% pyridine. no visible solids other than a trace of film on liquid surface. 9 Same as Test No. 7 above plus Same as in Test No. 8 above.

0.5% pyridine.

1 Butyrolactone.

It will be seen from the results of these qualitative tests that inhibition of polymerization of diacetylene is achieved with as little as 0.1% of pyridine. While the preceding example has illustrated a specific embodiment of the invention, substantial variations may be made without departing from the scope thereof. For example, the quantity of pyridine used to inhibit the polymerization of diacetylene can be varied widely, although the amount used depends somewhat on the amount of diacetylene present and the degree of inhibition desired. In general, only minor quantities of the inhibitor are required. Concentrations in the range of about 0.01% to about 5% by Weight of the total composition are suitable, with concentrations from about 0.1% to about 1% being preferred. The stabilizing agent may, of course, be employed in as great a concentration as desired.

The inhibitor of the invention is not restricted to use with butyrolactone as set out in the example above.

I Pyridine may be used to inhibit the polymerization of diacetylene in other like organic solvents. In solvent systems where such solvents are used to absorb acetylene from-agas stream containing it in combination with other gases including diacetylene,polymerization of the diacetylene is effectively inhibited by the presence of a minor amount of pyridine. To inhibit polymer formation during the absorption-stripping operation, the inhibitor can be added directly to the solvent feed stream, or it may be introduced as a solution of the desired concentration at some point in the absorption system. The inhibiting power of the pyridine is notafiected by continual reuse; hence, recirculation of the solvent provides as effective inhibition as does the introduction of the fresh solution. t

The inhibitor of the invention may also be utilized for preparing stabilized compositions of diacetylene in a solvent which can be safely stored over a period of time without undergoing polymerization with its usual attendant hazards.

What is claimed is:

l. A composition of matter consisting essentially of diacetylene dissolved in butyrolactone, and containing 1 pyridine in an amount from about 0.01% to about 5% by weight of the total composition.

2; A composition of matter consisting essentially of V diacetylene dissolved in butyrolactone, and containing pyridine in an amount from about 0.1% to about 1% by weight of the total composition.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A COMPOSITION OF MATTER CONSISTING ESSENTIALLY OF DIACETYLENE DISSOLVED IN BUTYROLACTONE, AND CONTAINING PYRIDINE IN AN AMOUNT FROM ABOUT 0.01% TO ABOUT 5% BY WEIGHT OF THE TOTAL COMPOSITION. 